Because Burke isn't top of the tree for the sex for tuition racket, it was already in existence before him and he is just the current faculty overseer, just like Quinn is only the current student leader of it. The racket is the main source of money for the college (they get funding on top of the tuition the girls receive) and has been going since the founding of the college and is currently being run by the lawyer of one of the founding families.
Considering how much, overall, Colleges in the USA get from the student base. Say B&R has, roughly, 5k students. Each pays 25k per anum. That is 125,000,000 smackaroos. Then, of course, you have federal/local government funding. Can't forget the foreign students who pay up to three times more than the average local student. Then are all kinds of grants and donations etc. So, yeah, this scheme for tuition that is going on, even with drugs including, is no way the main source of income for the College. More like pocket change comparatively speaking.